155/85R15 vs 165/85R15
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/85R15 | 165/85R15 | Change |
|---|---|---|---|
| Overall height | 25.4" | 26.0" | +2.6 % |
| Sidewall | 5.19" | 5.52" | +6.5 % |
| Section width | 155 mm | 165 mm | +6.5 % |
| Circumference | 79.7" | 81.8" | +2.6 % |
| Revs per mile | 795 | 774 | -2.6 % |
| Axle height | 12.69" | 13.02" | +8.5 mm |
| Approved rim width | 4–5.5" | 4.5–6" | overlap 4.5–5.5" |
Both are approved on a rim 4.5" to 5.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 155/85R15. Fit 165/85R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,264 on the road, so it under-counts by 264. At a true 70 mph the first turns 927 times a minute, the second 903.